An RFID (Radio Frequency Identification) label or tag is advantageously capable of being read and written high-capability data in a non-contact manner and resistant to the influence of dirt and dust. Thus, an RFID technology is continuously used as a substitute for existing barcode technologies.
However, there is a demand to use both barcodes and RFID tags practically in stores. To meet such a demand, an RFID tag writing system is provided which is capable of printing basic commodity data such as a commodity a name, a price, and a barcode on a label and writing the basic data and other detailed data in an RFID tag embedded in the label.
In a conventional calibration carried out in an RFID tag writing system, the setting of an electromagnetic wave transmission power of and an optimal writing position for RFID labels having different features is relatively cumbersome and needs to be manually done by professionals using special tools. Thus, normal users cannot conduct the calibration.
Further, an automatic calibration device is provided to solve the problem above. The device calculates an optimal writing position by conveying RFID labels by a specific feeding distance. However, the feeding of a whole label takes a long time, and the transmission power of an electromagnetic wave and a dynamic range of an AGC (Automatic Gain Control) section at a receiving side are not taken into consideration. Thus, the following problems are encountered.
Even though an optimal writing position is calculated through the calibration, if the electromagnetic wave output from an RFID reader-writer is too powerful, the electromagnetic wave will flow also through an RFID tag embedded in another label. Consequentially, the RFID reader-writer receives a response from a plurality of RFID tags. In this case, it may happen that data cannot be written to a target RFID tag to which data is to be written or the same information is written to a plurality of RFID tags. In addition, an optimal writing position may not be found if the power of the electromagnetic wave output from an RFID reader-writer is too weak. As a result, the setting of optimal writing parameters may take a long time even if an automatic calibration is employed.
Further, in the conventional RFID tag writing system, when an AGC function is employed, data can be written to a defective RFID tag which will cause a fault in an actual application because of a receiving level (the response output of an RFID tag) being lower than a normal value. In this case, the defective RFID tag will be issued as a normally-functioning tag, thus causing a problem that a defective RFID tag cannot be distinguished from normally-functioning RFID tags during such an issuing process.